1. Field
This application relates to the use of multiple charges to accelerate a projectile forward.
2. Detailed Description
Another way of explaining the traveling charge is as follows with four assumptions. The first assumption is that the barrier between two propellants (3) in FIG. 1 has no bore resistance. The second assumption is that the barrier creates a perfect seal between the first charge (4) and the traveling charge (2). The third assumption is that the propellant in the base charge (4) has the same mass as the propellant in the traveling charge (2). The fourth assumption is that both propellants have an identical burn rate.
If the base charge is the only charge ignited the pressure inside the chamber is illustrated in FIG. 12. Initially the base charge is a solid, but as the base charge burns it creates gas and heat, which increases the pressure. The ideal gas law states that PV=nRT. This can be rewritten that P=nRTN: P is pressure, n is the number of moles of gas, R is the universal gas constant, T is the temperature of the Kelvin, and V is the volume of the container. (The temperature cannot be increased beyond the burn temperature of the propellant, and the volume is increasing as the projectile travels down the bore, and the value n is increasing as long as the propellant is burning.) After a certain point, the rate of gas produced by the base charge is less than the rate of volume increase, which causes the pressure to decrease.
When the traveling charge is ignited, it produces another pressure wave pushing the projectile forward and the barrier back toward the breech end of the gun tube. This causes the volume between the barrier and the breach to decrease, which causes the pressure between the breech and barrier to increase. The increase in pressure allows the traveling charge to exert a greater average pressure on the projectile, which gives the projectile a higher muzzle velocity as shown in FIG. 13.
In this scenario the peak pressure inside the breech does not increase, but the average gas pressure in the gun tube is higher than with a single charge. The work done by the gas is equal to average pressure multiplied by the area of the base multiplied by the length of the gun tube. By increasing the average pressure, you increase the work done by the gas. The work of the gas is proportional to the mass times the velocity squared. Because of this a higher muzzle velocity is obtained.
Between the late 1940's and the late 1980's experiments were done trying to implement this technique, but none of them were successful. Due to the conditions inside the breech, the traveling charge experienced high pressure and temperature. This often caused the traveling charge to ignite prematurely. Premature ignition of the traveling charge led to excessive pressures in the gun tube resulting in breach blows or unpredictability in the muzzle velocity. Additionally, grain fracturing occurred. Due to the greater surface area created by the grain fracturing, the burn rate of the propellant increases. Since the degree of grain fracturing varied, the new burn time and the resulting exit velocity of the projectile was unpredictable. Even though the traveling charge increased the average pressure, it could not be utilized because of the lost control of the muzzle velocity and the danger of breech blows.
The difficulties of the traveling charge concept described above is overcome by the present invention. The unpredictability of the ignition time and burn rate of the charges is solved by insulating the booster charge from the effects of the base charge. For example, you could ignite the propellant closest to the projectile, called the base charge, first and then ignite the propellant nearest to the breech, called the booster charge. The barrier separating the two charges is structurally supported against the breech end of the gun tube. The barrier and related structural members isolate the booster charge form the pressures of the gas generated by ignition of the base charge. This is illustrated in FIG. 2 through FIG. 11. Upon ignition of the base charge, the projectile will be accelerated forward, increasing the volume between the barrier and the projectile.
When the barrier is opened, either through the one-way valve as in FIG. 2-FIG. 6 or a piston action as in FIGS. 7-9, the gas from the booster charge will combine with the gas from the base charge. This allows the average pressure to increase without surpassing the peak pressure that the breech can withstand, and will increase the maximum velocity of an artillery piece. This will result in the following pressure vs. distance-traveled diagram shown in FIG. 14.
The use of a one-way valve or piston produces an Insulated Secondary Ballistic Charges that yields the same benefits as the traveling charge effect while also eliminating the problems experienced in a traveling charge. Since the barrier is mechanically supported, an effective seal can be created between the first and the second charge, and the base charge will not damage the booster charge. This will eliminate the risk or pre-mature ignition and grain fracturing due to the increase in temperature and pressure.